1. Field of the Invention
The present invention relates to a color image reader installed on an image data reader such as a hand scanner, and more particularly to a color image reader that reads color image data using a 3-line color sensor.
2. Description of the Related Art
FIG. 16 shows the configuration of a storage-type photoelectric conversion device that reads color images. A 3-line color sensor 100 shown in FIG. 16 has linear image sensors 102B, 102G, and 102R, each with a plurality of linearly-arranged light receiving cells 101, arranged in parallel on the board. A blue filter 103B, a green filter 103G, and a red filter 103R are installed on the surface of each cell column.
On an image data reader with a fixed color image reader including the 3-line color sensor 100, a document containing color images is moved by the transport mechanism, composed of a motor and a transport belt, into the direction perpendicular to the direction in which the cells are arranged on the 3-line color sensor 100. On the other hand, on an image data reader with a movable color image reader including the 3-line color sensor 100, the color image reader is moved by the transport mechanism so that the 3-line color sensor 100 can scan a fixed document.
As shown in FIG. 16, the linear image sensors 102B, 102G, and 102R are spaced a distance of D equivalent to the distance of a few lines corresponding to the resolution. For example, when the linear image sensors 102B, 102G, and 102R each have a resolution of 300 dpi, when the light receiving cell 101 is 8 xcexcm xc3x978 xcexcm in size, and when the linear image sensors 102B, 102G, and 102R are each spaced a distance equivalent to four lines, D is 32 xcexcm (that is, 4xc3x978 xcexcm).
The linear image sensor 102G reads a part of color images four lines away from the linear image sensor 102B. Similarly, the linear image sensor 102R reads a part Of color images four lines away from the linear image sensor 102G, and the linear image sensor 102R reads a part of color images eight lines away from the linear image sensor 102B.
FIG. 17 is a timing diagram showing the output from the linear image sensors 102R, 102G, and 102B when the document moves below the 3-line color sensor 100 one line at a constant speed within one unit of storage time. FIG. 18 is a diagram showing the read positions on the document. In FIG. 18, the document is read from top to bottom and the symbol {circle around (1)} indicates one line.
TG in FIG. 17 is a transfer gate signal controlling the storage time of images in the 3-line color sensor 100. As shown in FIG. 17, the linear image sensors 102R and 102B output, at a specific point in time, the fourth line before, and the fourth line after, the line output by the linear image sensor 102G, respectively.
That is, as shown in FIG. 18, when the linear image sensor 102G reads nth line, the linear image sensor 102R reads the (nxe2x88x924)th line and the linear image sensor 102B reads the (n+4)th line. In other words, when the linear image sensor 102G outputs data from the nth line, the linear image sensor 102R outputs data from the (nxe2x88x924)th line and the linear image sensor 102B outputs data from the (n+4)th line. While the linear image sensor 102G outputs data from the (nxe2x88x924)th line to the (n+5)th line, the linear image sensor 102R outputs data from the (nxe2x88x928)th line to the (n+1)th line and the linear image sensor 102B outputs data from the nth line to the (n+9)th line.
Therefore, when reading images with the use of the 3-line color sensor 100 shown above, it is required that a positional compensation of xc2x14 lines be made with respect to the linear image sensor 102G.
FIG. 19 is a diagram showing how positional compensation is made. For example, data output from the linear image sensors 102R, 102G, and 102B is once stored in the corresponding buffers. When the 3-line color sensor 100 reads data of the nth line, which was output by the linear image sensor 102G, from the buffer memory, it also reads data, which was output by the linear image sensor 102R before the period of time equivalent to four lines, from the buffer memory (see the arrow in FIG. 18). Similarly, the 3-line color sensor 100 reads data, which was output by the linear image sensor 102B after the period of time equivalent to four lines, from the buffer memory (see the arrow in FIG. 18). This read method allows the R, G, and B data on the same line to be read at the same time. It should be noted that, instead of controlling the positions of the buffer memory from which data is to be read, the timing of writing data into the buffer memory may be controlled.
When the read speed is constant, positional compensation may easily be performed for R, G, and B data as described above. However, for a color image reader, such as a hand scanner, which does not always scan data at a constant speed, positional compensation may not be performed simply by changing the positions of the buffer memory from which data is to be read.
Consider a case, such as the one shown in FIG. 20, in which the read speed is not constant. In FIG. 20, the vertical line indicates the distance for which the image reader moves over the read object. Each box in the figure indicates one unit of storage time of the photoelectric conversion device. For example, the box xe2x80x9cC(nxe2x88x926)xe2x80x9d in the R column indicates that the image reader moves over two lines within one unit of storage time. In this case, the image reader moves two times faster than it does over xe2x80x9cC(nxe2x88x927)xe2x80x9d.
xe2x80x9cC(n+x)xe2x80x9d indicates image data output by the linear image sensors 102R, 102G, and 102B. In FIG. 20, the numeric value (nxc2x1x) in each frame indicates, not the number of lines on a read object such as a document, but the number of lines output by the photoelectric conversion device. For example, when the storage time of the photoelectric conversion device is 2 ms, the numeric value indicates the number of lines output every 2 ms.
In this case, the R data and the B data, which are four lines before and after the G data output by the linear image sensor 102G, cannot be used for positional compensation as for constant speed reading. Instead, as shown in FIG. 20, the G data C(n) on the nth line must be made to correspond to the R data C(nxe2x88x921) on the (nxe2x88x921)th line and to the B data C(n+2) on the (n+2)th line. That is, the correspondence among the R, G, and B data is not fixed when the reading speed varies randomly.
Disclosed in Japanese Patent Laid-Open Publication No. Hei 8-163316 is a color image reader that performs positional compensation for R, G, and B data by measuring the document transport speed using a rotary encoder provided on the transport mechanism that transports the document to be read. However, the color image reader disclosed in that publication is not designed for variable-speed reading. It only gives the compensation amount for use when the read speed is changed.
As described above, it is difficult for a color image reader installed on an image data reader such as a hand scanner, whose read speed may change during document reading, to appropriately perform positional compensation for R, G, and B data. This problem remains unresolved.
It is an object of the present invention to provide a color image reader performing positional compensation for three colors, R, G, and B, appropriately according to the read speed, to prevent a difference in the three colors caused by the time lag.
The color image reader according to the present invention comprising comprises speed monitoring unit for monitoring a read speed of a read object; and positional compensation unit or circuit for compensating positions of image data of primary colors based on a monitoring result of the speed monitoring unit, the image data being output from the photoelectric conversion means.
The positional compensation unit may be configured such that it sequentially stores therein the image data of the primary colors, the image data being output from the photoelectric conversion device and, when outputting the image data of one of the primary colors with the one of primary colors as reference data, selects and outputs the image data of other primary colors from the stored image data according to the monitoring result of the speed monitoring unit, the image data of other primary colors corresponding to a position in the read object where the image data of the one of the primary colors was read.
The positional compensation unit may be configured such that it has a plurality of line memories for the image data of the primary colors and, when outputting the image data of one of the primary colors to be used as the reference data from the plurality of line memories, selects the line memories where the image data of other corresponding primary colors is stored according to the monitoring result of the speed monitoring unit, and outputs the image data from the selected line memories.
The speed monitoring unit may be configured such that it outputs relative values for a reference speed. In particular, the relative values are preferably natural numbers.
The positional compensation unit may be configured such that it performs operation on the relative values output from the speed monitoring unit to select the line memories where the image data of other primary colors is stored.
The positional compensation unit may be configured such that it comprises selectors outputting the image data of the primary colors from the line memories; a relative speed data storage unit storing therein the relative values output from the speed monitoring unit; and selector controllers selecting, when outputting the image data of the reference primary color from the line memories, the line memories where the image data of other primary colors is stored based on the relative speed data stored in the relative speed data storage unit, the relative speed data corresponding to the reference color image data, and sends selection signals to the selectors.
The color image reader may further comprises a secondary-scan direction resolution compensation unit that compensates a secondary-scan direction resolution of the image data of the primary colors output by the positional compensation unit.
The secondary-scan direction resolution compensation unit maybe configured such that it comprises data line memories storing therein the primary color image data output from the positional compensation unit; an output controller outputting the image data from the data line memories a number of times corresponding to the relative value for the reference speed received via the positional compensation unit; and a line density data storage unit storing therein line density data.
The color image reader is a hand scanner.